A conventional Wesco type fuel pump is shown in Japanese Unexamined Patent Publication No. 7-197896.
In accordance with this structure, the Wesco type fuel pump (herein after, simply referred to as a fuel pump) is constituted by a pump portion and an electric motor.
A pump housing and a pump cover opposingly connected with the pump housing are arranged in a lower side of a housing formed in a cylindrical shape, and these elements are arranged fixedly in a lower side of the housing.
The cylindrical pump chamber is formed by a closed-end circular recess portion which is provided in the pump housing and has an open lower side, and a pump cover flat portion which closes the circular recess portion. A fuel inflow passage being open downward and a discharge hole being open toward the inside of a motor chamber formed within the housing are formed in the pump chamber. An impeller corresponding to a turbine vane formed in a disc shape is rotatably arranged within the pump chamber, a plurality of blade grooves communicating the top and back sides of the impeller are provided in an outer peripheral portion of the impeller, the impeller is connected to a rotating shaft of the electric motor arranged within the motor chamber, and the impeller rotates within the pump chamber on the basis of the rotation of the electric motor.
Further, a fuel flow passage which faces to the blade grooves of the impeller, is open to the inside of the pump chamber and is in a circular arc shape is provided in a depressed shape in a lower surface of the pump housing forming the pump chamber, and the discharge hole is provided so as to be open to the fuel flow passage in a terminal end portion in a rotational direction of the impeller. On the other hand, a fuel flow passage which faces to the blade grooves of the impeller, is open to the inside of the pump chamber and is in the circular arc shape is provided in a depressed shape in an upper surface of the pump cover forming the pump chamber, and the fuel inflow passage is provided so as to be open to the fuel flow passage in a starting end portion in the rotational direction of the impeller.
In accordance with the fuel pump mentioned above, an electric current is applied to the electric motor and the electric motor is rotated, whereby the impeller rotates within the pump chamber, and a pressure difference is generated between the front and the rear of the blade groove of the impeller. The fuel is sucked into the pump chamber including the fuel flow passage through the fuel inflow passage by repeating the action mentioned above by means of a lot of blade grooves, and the pressure increased fuel is discharged from the pump chamber into the motor chamber via the discharge hole.
Further, the pressure increased fuel supplied within the motor chamber opens a check valve within the fuel discharge passage being open to the upper portion of the housing on the basis of the fuel pressure, and is supplied toward an external fuel injection valve.
On the other hand, in the Wesco type fuel pump mentioned above, there is provided with an air bleeding hole for preventing a vapor lock within the pump chamber, and this structure is disclosed in Japanese Unexamined Patent Publication No. 9-209864.
In this case, an upper side of the air bleeding hole is formed so as to be open to the pump chamber via the fuel flow passage provided in the pump cover, and a lower side thereof is provided so as to be open outward from the pump cover.
Accordingly, a vapor generated within the pump chamber is discharged out of the pump chamber via the air bleeding hole together with the pressure increased fuel (corresponding to only a small part of the fuel) within the pump chamber, and it is possible to prevent the vapor lock from being generated within the pump chamber.
In accordance with the conventional Wesco type fuel pump mentioned above, in the case that the fuel pump is arranged within the fuel tank, and a fuel liquid surface formed within the fuel tank is lower than an opening of the fuel inflow passage formed in the pump cover, the following problems are generated.
In the case that the fuel pump is stopped in accordance with an engine stop in the state mentioned above, the check valve within the fuel discharge passage provided in the upper portion of the housing automatically closes the fuel discharge passage on the basis of a disappearance of the fuel pressure applied outward, and prevents the fuel within the downstream side of the fuel pipe than the check valve from flowing back toward the inside of the fuel pump.
On the other hand, in the state mentioned above, the fuel liquid surface within the fuel tank exists at a lower position than the lower opening of the fuel inflow passage and the lower opening of the air bleeding hole, whereby the air existing above the fuel liquid surface flows into the pump chamber from the air bleeding hole, and the fuel existing within the pump chamber is discharged into the fuel tank via the fuel inflow passage. Further, the air flowing into the pump chamber in the manner mentioned above flows into the motor chamber via the blade grooves of the impeller, the fuel flow passage of the pump housing and the discharge hole, the air is replaced by the fuel within the motor chamber gradually, and the fuel within the motor chamber is discharged into the fuel tank via the discharge hole, the pump chamber and the fuel inflow passage.
In accordance with the structure mentioned above, there is a risk that the motor chamber becomes empty without fuel in accordance with a passage of time after the engine stops.
Further, in the case that the engine starting operation is again carried out and the fuel pump is driven, in the state of no fuel within the motor chamber, the fuel discharged from the pump chamber via the discharge hole first fills up the motor chamber with the fuel so as to increase the pressure, and is thereafter supplied toward the fuel injection valve from the fuel discharge passage.
A remarkable matter here is that a volumetric capacity of the motor chamber is far larger than a volumetric capacity of the pump chamber. In other words, the motor chamber having the larger volumetric capacity is first filled with the fuel upon restarting the engine, long time is required until the fuel pressure within the motor chamber is increased, and the fuel supply to the fuel injection valve is delayed, so that there is a risk that an good restarting property of the engine is hampered.
Further, in the case that the fuel pump is arranged within the various fuel tanks, the fuel pump may be arranged in all directions such as in a vertical direction, a diagonal direction and a horizontal direction in view of a layout of the fuel pump. Therefore, differences occur in an air inflow into the pump chamber from the air bleeding hole according to the various arrangement states mentioned above, residual fuel within the pump chamber is uneven, and it is impossible to obtain a stable engine restarting property.
On the other hand, in accordance with Japanese Unexamined Patent Publication No. 2001-27160, there is disclosed a structure in which the check valve is arranged in the discharge hole, and the pressure within the motor chamber is held at a time when the fuel pump is stopped. However, in accordance with this structure, the number of parts and assembling man-hours are increased, whereby it is impossible to reduce a manufacturing cost, and it is hard to design the arrangement of the check valve with in an arrow discharge hole.